Hi--
I have a few corrections for you below:
On 4/28/20 9:41 AM, Qais Yousef wrote:
> Uclamp exposes 3 sysctl knobs:
>
> * sched_util_clamp_min
> * sched_util_clamp_max
> * sched_util_clamp_min_rt_default
>
> Document them in sysctl/kernel.rst.
>
> Signed-off-by: Qais Yousef <qais.you...@arm.com>
> CC: Jonathan Corbet <cor...@lwn.net>
> CC: Juri Lelli <juri.le...@redhat.com>
> CC: Vincent Guittot <vincent.guit...@linaro.org>
> CC: Dietmar Eggemann <dietmar.eggem...@arm.com>
> CC: Steven Rostedt <rost...@goodmis.org>
> CC: Ben Segall <bseg...@google.com>
> CC: Mel Gorman <mgor...@suse.de>
> CC: Luis Chamberlain <mcg...@kernel.org>
> CC: Kees Cook <keesc...@chromium.org>
> CC: Iurii Zaikin <yzai...@google.com>
> CC: Quentin Perret <qper...@google.com>
> CC: Valentin Schneider <valentin.schnei...@arm.com>
> CC: Patrick Bellasi <patrick.bell...@matbug.net>
> CC: Pavan Kondeti <pkond...@codeaurora.org>
> CC: linux-...@vger.kernel.org
> CC: linux-kernel@vger.kernel.org
> CC: linux-fsde...@vger.kernel.org
> ---
> Documentation/admin-guide/sysctl/kernel.rst | 48 +++++++++++++++++++++
> 1 file changed, 48 insertions(+)
>
> diff --git a/Documentation/admin-guide/sysctl/kernel.rst
> b/Documentation/admin-guide/sysctl/kernel.rst
> index 0d427fd10941..e7255f71493c 100644
> --- a/Documentation/admin-guide/sysctl/kernel.rst
> +++ b/Documentation/admin-guide/sysctl/kernel.rst
> @@ -940,6 +940,54 @@ Enables/disables scheduler statistics. Enabling this
> feature
> incurs a small amount of overhead in the scheduler but is
> useful for debugging and performance tuning.
>
> +sched_util_clamp_min:
> +=====================
> +
> +Max allowed *minimum* utilization.
> +
> +Default value is SCHED_CAPACITY_SCALE (1024), which is the maximum possible
> +value.
> +
> +It means that any requested uclamp.min value cannot be greater than
> +sched_util_clamp_min, ie: it is restricted to the range
i.e., it is
> +[0:sched_util_clamp_min].
> +
> +sched_util_clamp_max:
> +=====================
> +
> +Max allowed *maximum* utilization.
> +
> +Default value is SCHED_CAPACITY_SCALE (1024), which is the maximum possible
> +value.
> +
> +It means that any requested uclamp.max value cannot be greater than
> +sched_util_clamp_max, ie: it is restricted to the range
i.e., it is
> +[0:sched_util_clamp_max].
> +
> +sched_util_clamp_min_rt_default:
> +================================
> +
> +By default Linux is tuned for performance. Which means that RT tasks always
> run
> +at the highest frequency and most capable (highest capacity) CPU (in
> +heterogeneous systems).
> +
> +Uclamp achieves this by setting the requested uclamp.min of all RT tasks to
> +SCHED_CAPACITY_SCALE (1024) by default. Which effectively boosts the tasks to
by default, which
> +run at the highest frequency and bias them to run on the biggest CPU.
biases them
> +
> +This knob allows admins to change the default behavior when uclamp is being
> +used. In battery powered devices particularly, running at the maximum
> +capacity and frequency will increase energy consumption and shorten the
> battery
> +life.
> +
> +This knob is only effective for RT tasks which the user hasn't modified their
> +requested uclamp.min value via sched_setattr() syscall.
> +
> +This knob will not escape the constraint imposed by sched_util_clamp_min
> +defined above.
> +
> +Any modification is applied lazily on the next opportunity the scheduler
> needs
> +to calculate the effective value of uclamp.min of the task.
>
> seccomp
> =======
>
thanks.
--
~Randy
